When cutting a steel plate or a stainless steel plate in a curved line, a numerical controlled plate cutting device is generally used. This plate cutting device has a moving stand (which runs on a track of the main body of the plate cutting device) and a cross-shifting stand (which shifts in a direction perpendicular to the moving stand's running direction). The cross-shifting stand has a vertical arm orthogonal to the surface of the plate, and a torch or torches for cutting the plate vertically or aslant (a bevel cut) are attached at the end of the arm. The plate cutting device also has a torch inclining device for inclining the torch to bevel angles, and a torch swinging device for maintaining the bevel angle in a direction normal to the tangential direction of the curved cutting line.
If the cutting torch is a gas cutting torch, the torch is coupled to a gas supply hose and an oxygen 10 supply hose, the ends of which are connected to gas distributors disposed in the main body of the plate cutting device. If the cutting torch is a plasma cutting torch, the torch is coupled to plasma gas supply hose, a power source cord for supplying electricity to electrodes in the torch, and a cooling water supplying hose, the ends of which are also connected to gas distributors and an electric power source in the main body of the plate cutting device. As explained above, this kind of cutting torch always has hoses or cords the ends of which are fixed to the main body of the cutting device such as the moving stand.
When swinging such a plate cutting torch to keep it pointing in a direction normal to the tangential direction of the curved cutting line, the hoses and cords twist with the swing of the cutting torch. Because this twist biases the swinging device in a direction reverse to the direction of the swinging movement of the torch, there occurs the problem wherein the torch swinging device needs a powerful motor, or the swing range of the cutting torch is limited.